Heated pane

ABSTRACT

A heated window consisting of at least one rigid pane, at least two current busbars of different polarity placed substantially parallel close to one edge of the heated window at different distances from the edge and linear heating resistors electrically connected thereto, characterized in that the busbars lie sideways to the heating resistors and the heating resistors ( 2 ) start from a first current busbar ( 4 ) and, passing over the other current busbar ( 3 ) while being insulated therefrom, in the direction of the window surface and in at least one loop, return toward the other current busbar ( 3 ) and are electrically connected thereto.

[0001] The invention relates to a heated window consisting of at leastone rigid pane, at least two current busbars of different polarityplaced substantially parallel close to one edge of the heated window atdifferent distances from the edge, and linear heating resistorselectrically connected thereto.

[0002] These features are known from German utility model DE 296 06 071U1, which relates to a laminated window with electric heating, in whichheating resistors are provided electrically mounted in parallel andembedded in the intermediate thermoplastic layer in the region of therest position of the windshield wipers. Also, metal film strips actingas busbars connected to electrical power supply lines, and which areelectrically connected to the heating resistors, are embedded in theintermediate thermoplastic layer. The busbars are arranged very close toeach other and the heating resistors are placed, in the form of loops,between the busbars. In one embodiment, the heating resistors arearranged as U-shaped loops, one interleaved with the other in thehorizontal direction and brazed to two ribbon-shaped current busbars.The current busbars are very close and parallel to each other in theregion of one side edge of the windshield. The current busbar away fromthe edge of the windshield is only about half as long as the currentbusbar placed in the immediate proximity of the side edge, this currentbusbar being connected to the upper halves of the wire loops, and theother current busbar being connected to the lower halves of the wireloops.

[0003] A windshield with electric heating provided with a flat heater,with two current busbars placed at the opposite upper and lower edges ofthe window is known from EP 0 479 154 A1. The lower current busbar isprovided in the middle with a current lead oriented perpendicularly tothe edge of the window, therefore in the shape of a T. The upper currentbusbar is connected to two leads, which are placed along the two sideedges. The two leads further extend along the lower edge of the windowbelow the lower current busbar. The first lead transversely crosses,under electrical insulation, the perpendicular branch of the T and iselectrically connected to the other lead. The other lead is also takentoward the lower edge of the window. Because of this arrangement, onlytwo electrical connection lines are needed in the middle of the loweredge of the windshield.

[0004] The object of the invention is to produce another heated windowwith current busbars arranged close to one edge of the window.

[0005] According to the invention, this objective is achieved by thefact that the busbars lie sideways to the heating resistors and theheating resistors start from a first current busbar and, passing overthe other current busbar while being insulated therefrom, in thedirection of the window surface and in at least one loop, return towardthe other current busbar and are electrically connected thereto. Thecharacteristics of the secondary claims reveal the advantageousimprovements of this object.

[0006] According to the invention, the heating resistors extend from onecurrent busbar away from the edge in the direction of the face to beheated and they return back in a loop toward another current busbarclose to the edge, crossing the current busbar away from the edge. Thecurrent busbars close to and away from the edge are arranged in theregion of the same edge of the window. To prevent a short circuit, theheating resistor is electrically insulated from the current busbar inthe region of the crossing. The heating resistors thus arranged form aheating field, which lies over a particular zone of the heated windowand which is supplied with electrical energy by the pair of currentbusbars.

[0007] The invention is not limited to the fact that there is only asingle heating field on the heated window. It may, for example, bebeneficial to provide several heating fields, especially to producedifferent heating powers in particular zones. It is thus possible toimagine arranging two or more than two heating fields side by side inthe face of the window. The respective pairs of current busbars, forexample, for two heating fields, may be at the same edge of the window,the current leads coming from the upper edge for a first upper heatingfield, and from the lower edge for the other lower heating field. If thecurrent lead must be effected from a single edge of the window, it isnecessary to cross, in an insulated manner, more than one currentbusbar. In another variant, it is possible to use one current busbar asa common ground terminal for the two heating fields. Furthermore, it ispossible to arrange the pairs of busbars for different heating fields atdifferent side edges. The heating fields then cover zones of the heatedwindow, which are arranged at a distance from each other, are contiguousor even are interleaved with each other.

[0008] In another variant of the heated window, the heating resistorsform several loops, before returning to the other current busbar. Theheating resistors therefore do not extend only from the busbar away fromthe edge over the width of the heating field to return again toward thebusbar close to the edge, but they go back into at least another loopagain over the width of the heating field toward the pair of busbars.Therefore there is always an odd number of conducting loops. For aspecific heating resistor, which depends on the length of the conductor,on the cross section of the conductor and on the specific resistance ofthe material used, it is possible to adjust the heating power per unitarea by choosing the number of loops, independently of the geometricaldimensions of the surface to be heated. The use of a greater number ofloops has the additional advantage that the number of electricalconnections, which in general must be produced by brazing, is smallerthan when arranging the heating resistors in a single loop each time. Itis thus possible to save on the number of working steps.

[0009] The heated windows according to the invention may be monolithicwindows, in which the heating resistors are placed on one of their mainfaces. A known example of this type of window is supplied by motorvehicle windows or by toughened safety-glass windows, which are providedwith heating resistors made of a conducting matrix. Normally, aconducting ceramic paste with a high silver content is screen printed inthe shape desired for the heating conductors and the conducting busbarson the surface of the window for this purpose, and it is then baked. Theconducting busbar away from the edge can be insulated from the conductorwhich crosses it by means of a dielectric matrix. For this purpose, theprinting operation for the heating resistors and the busbars must besplit into two steps. In a first step, the current busbar away from theedge is printed with the heating resistors, and the return branch of theloop of the heating conductor terminates slightly before the currentbusbar away from the edge. The second step follows, in which aninsulating layer, for example a dielectric matrix to be baked, isarranged on this current busbar. Next, the current busbar close to theedge is printed, and the connecting conductors are placed at the sametime toward the open ends of the loops of the heating conductors. Theconnecting conductors cross, in an insulated manner, the busbar awayfrom the edge and close the electric circuit of each individual heatingresistor loop.

[0010] A series of printed conducting and insulating layers is knownfrom German patent DE 39 11 178 C2. In this case, an output antennaconductor is made in the form of a coaxial pseudoconductor with powerfulshielding.

[0011] Apart from monolithic heated windows, the invention alsocomprises heated windows made of laminated glass, which consist of atleast two rigid panes assembled to each other by adhesive bonding bymeans of an intermediate layer. In this case, the heating resistors arepreferably composed of metal wires, which are embedded in theintermediate layer. However, it is also possible to manufacture a heatedlaminated window according to the invention by using the monolithicheated window described in order to form one of the individual panes.The surface with the heating resistors may just as well be placed on theinside as on the outside of the laminated glass. The individual panesmay consist of glass or of plastic. The laminated windows may becomposed of two or more panes of identical or different materials.Normally, an adhesive thermoplastic film, for example made of polyvinylbutyral, is used as an intermediate layer assembling the individualpanes to each other.

[0012] The current busbars in the laminated windows, which may be heatedby means of heating resistors embedded in the intermediate layer,normally consist of flat metal films made of tinned copper. There arealso models which are further provided with an insulating coating madeof polyimide. With a metal film strip of this sort acting as a currentbusbar away from the edge, a laminated window according to the inventionmay be easily manufactured by removing the insulator only at thelocations where the heating resistors must be electrically connected tothe current busbar. The current busbar close to the edge may be placedwithout an insulating coating or, where an insulated metal film strip isused, the insulator may also be removed at its locations of connectionwith the heating resistors.

[0013] To ensure that vision through the laminated window is hindered aslittle as possible, the heating wires must have a relatively smalldiameter of about 20 μm to 100 μm. Heating wires made of tungsten haveproved to be suitable for this purpose. However, copper wires, which canbe provided with a layer of a dark matt color in order to preventmetallic reflections, are also suitable to be used in the laminatedwindow according to the invention. Wires with several layers are alsoknown, which have a mechanically strong core which is enveloped by ametal which is a good conductor and/or easy to braze. The material forthe wires and/or the diameter of the wires is chosen according tomechanical and electrical requirements associated with the desiredheating field.

[0014] When the wires are straight and arranged in parallel at a shortdistance from each other, phenomena of diffraction on incidence of thelight may occur under unfavorable circumstances. Such phenomena can beprevented by certain irregularities in the alignment of the heatingwires, for example a wavy arrangement of the heating wires.

[0015] When the current busbars are only arranged close to a single sideedge, the laminated window is suitable, for example, for use as a heatedlaminated window with free edges, therefore for example as a motorvehicle side window which can be opened. The current busbars can bearranged inside the well of the door and be masked by the bodywork orsealing elements.

[0016] Other details and advantages of the subject of the invention willemerge, without any intention of limitation, from the drawing of oneembodiment and from its detailed description which follows.

[0017] In the drawings, which constitute a simplified representationwithout a particular scale,

[0018]FIG. 1 shows a laminated window according to the invention as aside window of a motor vehicle, in elevation; and

[0019]FIG. 2 shows a section through the side window of FIG. 1 along theline I-I.

[0020] According to FIG. 1, a laminated window 1 is provided withheating wires 2 made of black lacquered copper, which are placed insidethe laminated window 1 and whose diameter is about 85 μm. The heatingwires 2 lie in the shape of a loop between the lower edge of the sidewindow 1 in the fitted position and its upper edge. In order to supplyit with electricity, a first end of each loop is connected to a currentbusbar 3 and the other end of the loop is connected to the currentbusbar 4. On the path toward the current busbar 4, the heating wires 2must cross the current busbar 3 in the zones 31. In these zones 31, theheating wires 2 are electrically insulated from the current busbar 3.The two current busbars 3 and 4 are, like the heating wires 2, placedinside the laminated window 1 and are connected to the two poles of anon-board electrical network. Normally, there is a voltage of 12 Vbetween the current busbars. The current supplied complies with theheating power needed per unit area, for which it is necessary to takeinto account the electrical resistance of the heating wires 2 and theirmutual separation. In order to distribute the heating power constantlyover the face of the laminated window 1, the length of the wires of theindividual loops must also be as equal as possible, the other propertiesof the wires being equal. Consequently, for the laminated window shownin FIG. 1, the portion of wire which is in the region of the inclinededge and therefore of lower height has been arranged in a loop with fivechanges of direction, while each of the other portions of wire changedirection only three times.

[0021] The current busbars 3 and 4 leave the laminated window 1 at theside and are connected in a known manner to the on-board network. Forthe car side window shown here, the part next to the lower edge of thewindow, in which the current busbars are located, is arranged inside thedoor well and is thus masked by the bodywork. Moreover, the normalmasking of the current busbars using layers of an opaque color is notnecessary in this case.

[0022]FIG. 2 shows a representation in section of the side window ofFIG. 1 along the line I-I. The laminated window 1 is composed of twoindividual panes 11 and 12 with a thickness of about 2.1 mm, which areassembled to each other in a known manner by adhesive bonding withinsertion of an intermediate thermoplastic layer 13 made of polyvinylbutyral. Before the assembly operation, the heating wires 2 and thecurrent busbars 3 and 4 are embedded in the surface of the intermediatelayer 13 using a method which is also known.

[0023] The current busbar 4 is composed of a tinned copper film and ismechanically and electrically connected to the heating wire 2 bybrazing. In contrast, for the current busbar 3, a tinned copper film 32is surrounded on all sides by an insulating coating 33 made ofpolyimide. The heating wire 2 can therefore cross the current busbar 3,where it will certainly touch it but nevertheless will have noelectrical contact therewith. At the locations where the heating wire 2is electrically connected to the current busbar 3, the insulatingcoating must be removed before encapsulation in the intermediatethermoplastic layer.

1. A heated window consisting of at least one rigid pane, at least twocurrent busbars of different polarity placed substantially parallelclose to one edge of the heated window at different distances from theedge, and linear heating resistors electrically connected thereto,characterized in that the busbars lie sideways to the heating resistorsand the heating resistors (2), start from a first current busbar (4),and, passing over the other current busbar (3) while being insulatedtherefrom, in the direction of the window surface and in at least oneloop, return toward the other current busbar (3) and are electricallyconnected thereto.
 2. The heated window as claimed in claim 1,characterized in that the heating resistors (2) return toward the othercurrent busbar (3) after having formed more than one loop and areelectrically connected thereto.
 3. The heated window as claimed in claim1 or 2, characterized in that the rigid pane is a glass pane and theheating resistors (2) consist of a baked conducting ceramic matrix. 4.The heated window as claimed in claim 1 or 2, characterized in that itconsists of a laminated window (1) formed from at least two rigid panes(11, 12) assembled to each other by adhesive bonding by means of anintermediate layer (13).
 5. The heated window as claimed in claim 4,characterized in that the heating resistors (2) are embedded in theintermediate layer (13) and in that the current busbars (3, 4) arestrips of metal film.
 6. The heated window as claimed in claim 5,characterized in that at least one metal film strip (3) is surroundedwith an insulating sheath (33), which is only broken in the region ofthe electrical connection with a heating resistor (2).
 7. The heatedwindow as claimed in either of claims 5 and 6, characterized in that theheating resistors (2) consist of tungsten wire.
 8. The heated window asclaimed in either of claims 5 and 6, characterized in that the heatingresistors (2) consist of copper wire, in particular of black-lacqueredcopper wire.
 9. The heated window as claimed in either of claims 5 and6, characterized in that the heating resistors (2) are composed ofseveral conducting materials, in particular of a first mechanicallystrong metal and a second metal having a higher electrical conductivityand good brazability.
 10. The heated window as claimed in any one ofclaims 5 to 9, characterized in that the heating resistors (2) areembedded in the intermediate layer (13) in a wavy arrangement.
 11. Theheated window as claimed in any one of claims 5 to 9, characterized inthat the heating resistors (2) are embedded in the intermediate layer(13) in a straight, and therefore not wavy, arrangement.
 12. The heatedwindow as claimed in any one of claims 5 to 11, characterized in that atleast one of the panes (11, 12) is made of glass.
 13. The heated windowas claimed in any one of claims 5 to 12, characterized in that theintermediate layer (13) is a thermoplastic polymer, in particularpolyvinyl butyral.
 14. The heated window as claimed in any one of thepreceding claims, characterized in that the heated window (1) is a motorvehicle side window which can be opened and in that the current busbars(3, 4) are arranged in a masked position.